In a communication receiver, a received RF signal is demodulated to generate a baseband signal waveform containing a self-clocking bit stream of digital data. The baseband signal waveform is tracked using a timing recovery loop. The timing recovery loop tracks bit timing of the baseband signal waveform and generates timing pulses, which are then used in a data detector for sampling the baseband signal waveform at the bit intervals for reconstructing the digital bit stream from the received baseband signal waveform. The baseband signal waveform is subject to channel noise leading to poorly generated timing pulses and hence poor bit timing resulting in poor data detection. When the timing recovery loop loses track, the bit stream is no longer detected. The bit stream is recovered using conventional timing recovery loops that are subject to bit timing lock drop in the timing recovery loop.
The conventional timing recovery loops use early-and-late gates, digital transition tracking, filter-and-square, and delay-and-multiply functions. In bit timing detection, the bit stream is self clocking and the timing differential dithers about correct bit timing in the timing recovery loops. For mobile environments, these timing recovery loops drop lock when the loop signal-to-noise ratio (SNR) is smaller than a threshold value or the residual Doppler frequency is larger than the operating loop bandwidth. Timing recovery loops use slow bandwidth phase lock loops that drop lock at low SNR. After dropping lock, the conventional timing recovery loops disadvantageously experience long hang up time due to the need to reacquire the timing pulses.
Random walk filters have been used for decades in various applications. In the past, random walk filters have been applied to digital phase synchronization systems. Random walk filters have been theoretically applied to carrier phase detection where differentials between local references and transmitter carriers results in a phase correction that is unidirectional and constantly circular over 360 degrees. Although used for decades, random walk filters have not been adapted to improving the bit clock locking stability in timing recovery loops. Random walk filters have not been applied to recover bit timing information of a digital data stream. Existing timing recover loops suffer from drop of bit timing lock in noisy channels. Noisy channels suffer from ambiguous bit timing transitions leading to jittering and inaccurate timing pulses. These and other disadvantages are solved or reduced using the invention.